Bump (Normal) Maps for FSX
Creating Bump (Normal) Maps with the nVidia plugin and Photoshop v7 or v8...
The Alpha channel is simply what WAS in the Red channel that's been cut-n-pasted to the Alpha channel, before the Green chanel's contents are "Inverted" (note: I don't mean "flipped," I mean that the entire image is "photo reverse image," i.e. "Invert"ed...
Here is the reason why. Compressing the image results in severe degradation of the normal information: in fact, the RGB vectors are no longer precisely 1 as they should be.
"There is another option, but it requires that your normal map be changed around a bit and also that your shader be edited slightly. DXT5 gives the most quality to the green channel and to the alpha channel. We can take advantage of this to "hijack" the DXT5 format and turn it into a normal map compression format. First we need to re-arrange the data in the normal map. Take the red channel data (X) and put it in the alpha channel. Now make the red and blue channels black 1. Now we need to adjust the shader to switch the data back around for us. The shader needs to be told that the red channel data is in the alpha channel of the texture and that it needs to calculate the blue channel values itself. This is possible with a little algebra because we can assume that the vector that results from R,G, and B will be unit length one. If you are able to make these changes to both the normal map and the shader, you'll get 4 to 1 normal map compression with very little quality loss!"
"Positive or Negative Y
When using Tangent Space normal maps, the most common difference in formats is the direction that the green channel is lit. Some programs light the green channel from the left (postive Y) and others light the green channel from the right (negative Y). Some programs give you the option to choose positive or negative Y. If your normal map isn't being lit correctly, the first thing that you should try is to flip the green channel. Just open the normal map in Photoshop, select the green channel, and choose "Invert." That will give you the same result as if you had rendered the normal map in the other format. "
BTW, if you want to learn more about FSX's version of "bump mapping," understand that it's more commonly known as "normal mapping." Actual "bump mapping" is generally a gray-scale image with no Alpha channel. "Normal mapping" on the other hand is an entirely different concept.
There's a very nice article here: http://en.wikipedia.org/wiki/Normal_mapping that explains this in greater detail. From what I've read so far, it's not clear to me that ACES themselves have fully exploited the potential in their own examples.
I haven't taken the time to read this "tutorial" in depth yet, but it looks promising!
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NOTE: Unless explicitly stated otherwise, everything written by my hand is MY opinion. I do NOT speak for any company, real or imagined...
Last edited by n4gix; 04 May 2008 at 00:32.
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